The purpose of this project is to assess the influence of the immunopotentiating agents BCG and C. Parvum on the mechanisms involved in securing the availability and promoting the recruitment of macrophage-forming cells into sites of tumors undergoing cellular attack. The macrophages in such tumor sites are believed to be necessary in the killing of tumor cells but virtually nothing is known about their immediate source of supply, the blood monocyte pool, the adequacy of which is essential for the expression of certain forms of cell-mediated immunity. Isotopic labeling studies will be carried out in mice, rats and guinea pigs grafted with syngeneic tumor tissue and in non-tumor bearing animals at varying intervals before, at the time of and after the systemic or intralesional injection of BCG or C. parvum. Data relating to the cytokinetics of monocyte production and the recruitment of macrophages will be obtained in relation to the respective treatments by means of autoradiography of cell smears and tissue sections and by other quantitative procedures. An analogous protocol will be adapated to animals immunologically impaired by thymus deprivation to study the influence of adoptively transferred specifically sensitized lymphocytes from syngeneic donors on mechanisms of macrophage mobilization. The interrelationships of the respective components will be correlated with respect to the fate of the tumors.